Self-expandable scaffolding device for the treatment of aneurysms

ABSTRACT

A stent comprises a first longitudinally extended cylindrical-shaped member. The first member comprises a plurality of first longitudinal struts and an array of first radial struts extending between the first longitudinal struts. The stent further comprises an overlapping region to form a dense mesh.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is continuation application of U.S. patent applicationSer. No. 15/655,674, filed on Jul. 20, 2017, now U.S. Pat. No.10,507,123, which is a continuation of International Application No.PCT/US2016/014191, filed Jan. 20, 2016, which claims the benefit of U.S.Provisional Application No. 62/105,432, filed Jan. 20, 2015, thecontents of all of which are hereby incorporated by reference in theirentirety.

TECHNICAL FIELD

This invention relates to endovascular devices such as stents for thetreatment of tissue defects such as aneurysms.

BACKGROUND

Tissue defects involve an absence of healthy tissue in a body area wheresuch tissue would normally be present. For example, a common tissuedefect includes aneurysms, in which there is a defect in a blood vesselwall that causes an outpouching of the vessel tissue. Aneurysm may formin disparate locations such as the aorta, iliac arteries, renalarteries, popliteal arteries, splenic arteries, femoral arteries, tibialarteries, and throughout the neurovasculature. Other common tissuedefects include arteriovenous fistulas, intestinal fistulas, colonicfistulas, anal fistulas, hernias and traumatic wounds. Aneurysms andother tissue defects may be treated using surgical methods, such asclipping, or endovascular methods, such as flow diversion techniquesusing a flow diverter (e.g., a covered stent) or coil embolizationtechniques using coils or a combination of coils and a stent.

In coil embolization techniques, small metallic coils are delivered tothe sac of an aneurysm. The coils pack the sac densely to limit bloodflow in the sac, thereby inducing clotting of the blood inside the sacand, eventually, healing of the aneurysm. However, such coilembolization techniques can be used only with aneurysms with a narrowneck region to hold the coil in place. Further, such coil embolizationtechniques suffer from complications, including the risk ofrecanalization in which blood flow returns to the sac and further swellsthe sac.

In coil embolization techniques using a combination of coils and astent, the stent is used as a device that acts as a scaffoldingstructure to keep the coil inside the aneurysm volume, as shown in FIGS.1A-B. After the stent is deployed covering the neck of the aneurysm, adelivery microcatheter is passed through a strut (also called anelement) of the stent into the aneurysm dome and embolic coils aredeployed through the catheter tip inside the aneurysm dome to fill theaneurysm volume.

A significant problem with coil embolization techniques is that duringthe process of filling the aneurysm volume, the coils or blood clots atthe embolization site sometimes herniate into the parent artery if thestent fails to provide adequate scaffolding. Coils or blood clotsherniating into the parent artery may escape from the aneurysm volumeand travel downstream into the blood vessel and cause a stroke or otherlife threatening complications.

Another technique for treating aneurysms is with the use of a flowdiverting stent. A flow diverter is placed in a blood vessel such thatit spans the neck region of an aneurysm, thereby diverting blood flowaway from the aneurysm sac. The stagnant blood inside the aneurysm sacmay then clot and the aneurysm may heal.

Flow diverters, however, also suffer from complications. Braided devicesused in the neurovasculature are bulky and often cannot access distalaneurysms. Use of these devices may also result in incomplete or delayedaneurysm occlusion, which can lead to delayed aneurysm rupture andstroke. In other vascular beds, such as the aorta or arteries of thelower extremities, covered stents are used to treat aneurysms. The mostcommonly used materials for covered stents includepolytetrafluorethylene (PTFE) and polyethylene terephthalate (PET). Bothof these materials add substantial bulk, making the stent unsuitable foruse in certain vascular beds, such as the neurovasculature. In addition,these materials tend to be impermeable or only semi-permeable. Thislimits tissue in-growth into the stent covering and leaves a foreignbody that is continuously exposed to blood. Because of this, there is along-term risk of acute thrombosis and stenosis inside the stent.Moreover, because these stents are impermeable to blood flow they willcut-off blood flow to any vessels adjacent to the aneurysm that arecovered with the stent. This can lead to ischemia of critical tissuessuch as the intestine. Further, blood clots formed at the covered stentimplanted site may dislodge and cause a heart attack, stroke, or otherlife threatening complications.

A significant problem with stents, whether used to provide scaffoldingto coils in coil embolization techniques or as a covered stent in flowdiversion techniques, is their tendency to kink and failing to achievegood wall apposition when placed in torturous vascular beds.Accordingly, there is a need in the art for improved stents that aremore kink resistant and achieve improved wall apposition, whilesimultaneously serving as a good scaffold for coil-based aneurysmtreatment techniques.

SUMMARY

In one or more embodiments, a stent includes a first longitudinallyextended cylinder having a C-shaped cross-section, the first cylinderincluding a plurality of first longitudinal struts and an array of firstradial struts extending between the first longitudinal struts, and asecond longitudinally extended cylinder having a C-shaped cross-section,the second cylinder including a plurality of second longitudinal strutsand an array of second radial struts extending between the secondlongitudinal struts. The first cylinder and the second cylinder areconfigured to form a dense mesh when assembled.

In some embodiments, the first cylinder and the second cylinder areassembled, and a part of the first cylinder and a part of the secondcylinder overlap to form the dense mesh. In some embodiments, more thanhalf of the first cylinder and more than half of the second cylinderoverlap to form the dense mesh.

In some embodiments, the second cylinder is disposed within the firstcylinder. In some embodiments, the first cylinder and the secondcylinder are aligned such that an opening of the first cylinder and anopening of the second cylinder are on opposing sides of the stentradially.

In some embodiments, the first cylinder and the second cylinder areattached at a joining location including a part of the firstlongitudinal struts and a part of the second longitudinal struts. Insome embodiments, the first cylinder and the second cylinder areattached at the joining location by winding a tube or a coil around thepart of the first longitudinal struts and the part of the secondlongitudinal struts. In some embodiments, the first cylinder and thesecond cylinder are attached at the joining location further by a solderdisposed within the wounded tube or coil. In some embodiments, the tubeor coil includes a radiopaque marker.

In some embodiments, the first and second radial struts include straightstruts, sinusoidal-shaped struts, or both. In some embodiments, thefirst and second longitudinal struts each include a central strut andtwo edge struts. In some embodiments, the first and second longitudinalstruts include S-shaped struts that connect to and extend from acorresponding central strut towards a corresponding edge strut, curvearound to extend towards the corresponding central strut, and curvearound to extend to and connect to the corresponding edge strut. In someembodiments, a take-off angle of the first radial struts from acorresponding one of the first longitudinal struts is between 15° to90°, and a take-off angle of the second radial struts from acorresponding one of the second longitudinal struts is between 15° to90°. In some embodiments, the first cylinder and the second cylinder aresame in shape.

In one or more embodiments, a stent includes a first longitudinallyextended cylindrical-shaped member, the first member including aplurality of first longitudinal struts and an array of first radialstruts extending between the first longitudinal struts. The stentincludes an overlapping region to form a dense mesh.

In some embodiments, the overlapping region includes a part of the firstmember overlapping around another part of the first member. In someembodiments, the overlapping region includes more than half of an outersurface of the stent.

In some embodiments, the first member has a C-shaped cross-section, andthe stent further includes a second longitudinally extendedcylindrical-shaped member having a C-shaped cross-section, the secondmember including a plurality of second longitudinal struts and an arrayof second radial struts extending between the second longitudinalstruts. The overlapping region is formed by overlapping at least a partof the first member and at least a part of the second member whenassembled.

In some embodiments, the first member and the second member areassembled, and the second member is disposed within the first member. Insome embodiments, the first member and the second member are alignedsuch that an opening of the first member and an opening of the secondmember are on opposing sides of the stent radially.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B illustrate use of a stent and an emboli coil for thetreatment of an intracranial aneurysm.

FIG. 2 is a diagrammatic perspective view of individual halves of astent according to an embodiment.

FIG. 3A is a diagrammatic perspective view of the individual halves ofthe stent of FIG. 2 aligned before assembly.

FIG. 3B is a diagrammatic cross-sectional view of the individual halvesof the stent of FIG. 2 aligned before assembly.

FIG. 4 is a diagrammatic flat pattern view of a first half of the stentof FIG. 2.

FIG. 5 is a diagrammatic flat pattern view of a second half of the stentof FIG. 2.

FIG. 6 is a diagrammatic flat pattern view showing the overlapping ofthe two halves of the stent of FIG. 2.

FIG. 7A is a diagrammatic flat pattern view of a stent having sinusoidalstruts according to an embodiment.

FIG. 7B is a diagrammatic flat pattern view of a stent having straightlongitudinal struts and sinusoidal radial struts according to anembodiment.

FIG. 7C is a diagrammatic flat pattern view of a stent having straightstruts according to an embodiment.

FIG. 8 is a diagrammatic cross-sectional view of a stent according to anembodiment.

FIG. 9 is a diagrammatic flat-pattern view of a part of a stentillustrating exemplary dimensions according to an embodiment.

FIG. 10A is a diagrammatic perspective view of a part of a stent with atube joining two halves of the stent according to an embodiment.

FIG. 10B is a diagrammatic perspective view of a part of a stent with awounded coil joining two halves of the stent according to an embodiment.

FIG. 11A is a diagrammatic perspective view of a part of a stent with asoldered tube according to an embodiment.

FIG. 11B is a diagrammatic perspective view of a part of a stent with asoldered wounded coil according to an embodiment.

FIG. 12 is a diagrammatic perspective view of a part of a stent with acrimped tube according to an embodiment.

Embodiments of the present disclosure and their advantages are bestunderstood by referring to the detailed description that follows. Itshould be appreciated that like reference numerals are used to identifylike elements illustrated in one or more of the figures, in which theshowings therein are for purposes of illustrating the embodiments andnot for purposes of limiting them.

DETAILED DESCRIPTION

By design, a stent is a cylindrical shape device that should becompactable so it can be delivered via a small delivery catheter andshould be flexible so it can be tracked through tortuous blood vesselsin the brain. A self-expandable stent is a type of stent that expands tothe diameter of the blood vessel after it has been deployed from thedelivery catheter. A self-expandable stent is made from a superelasticalloy such as an alloy of Nickel and Titanium, also called nitinol.

A self-expandable stent is made from a hypotube made with superelasticalloy material. The stent design is first drawn as a flat pattern (how astent would look like if sliced longitudinally and pressed flat) on aComputer-Aided-Design (CAD) software. The same design pattern of thestent is then created on the hypotube by cutting it on to the hypotubeusing a powerful laser beam. After performing a series ofpost-processing work (which removes much of material from the laser-cutstent to soften) on the laser-cut part, a final stent device with itsfinal specifications is produced. In order to deliver the stent deviceto its target location in the blood vessel, the stent must have adelivery system.

A stent delivery system can be a long wire with variable flexibilityprofile having some mechanism for attaching and detaching the stent.There are several mechanisms of detachment used in the market such aselectrolytic detachment, twist-type detachment or mechanical detachment.

A typical self-expandable stent is a one piece cylindrical device cutfrom a cylindrical hypotube of a superelastic alloy. In one or moreembodiments, a stent 100 is constructed with two parts 102, 104, eachpart representing one half of the stent and the design of one part 102being the mirror image of the other 104 as shown in FIG. 2. The firsthalf 102 is also referred to as a first cylinder 102 or a first member102, and the second half 104 is also referred to as a second cylinder104 or a second member 104. The first half 102 and the second half 104may be aligned and assembled such that the longitudinal strut 106 of thefirst half 102 and the longitudinal strut 108 of the second half 104 areon opposing sides of the stent 100, and the longitudinal opening offirst half 102 and longitudinal opening of second half 104 are onopposing sides of the stent 100.

After aligning the two parts 102, 104 together in the manner shown inFIGS. 3A-B, the final assembled stent 100 results in a dense strutstructure such as a dense mesh structure 110. The dense mesh structure110 of the stent 100 provides the scaffold for the retention of theembolic coils. At the same time, since the struts are not weaved intoeach other, the struts have the agility to move and provide a passage ifa catheter is to be passed through the mesh structure 110. To assemblethe two parts 102, 104 together, the longitudinal struts 106, 108 arealigned and subsequently joined by using either soldering, marker bandcrimping, polymer heat shrinking or any other method with abiocompatible material at, for example, location 112.

In one embodiment, the strut design of the first half 102 and the secondhalf 104 may be as shown in FIG. 4 and FIG. 5, respectively. FIG. 4 andFIG. 5 shows a complete design drawn as a flat pattern (representing howeach half 102, 104 would look if pressed flat) in the CAD software. Eachhalf 102, 104 consists of two different designs of radial struts(sinusoidal strut 6 and S-shaped strut 2-4) but arrayed multiple timesalong the length of the stent 100. One strut 6 runs directly fromlongitudinal strut 1 (such as longitudinal strut 106, 108), alsoreferred to as a central strut 1, to a longitudinal strut 5, alsoreferred to as an edge strut 5, at the other end. The strut 6 has asinusoidal shape for enhanced flexibility. The other strut 2-4 includesstruts 2, 3, and 4 and has an “S” shape as shown in FIG. 4. The “S”shaped strut originates from the longitudinal strut 1, transversesstraight as strut 2 towards the other longitudinal strut 5 at whichpoint it turns around and transverses the same length back as strut 3 inparallel to strut 2 and turns back one more time as strut 4 that runsparallel to strut 2 and 3 and finally connects to the other longitudinalstrut 5. This S-shaped strut 2-4 adds to the overall flexibility of thedevice 100 and advantageously provides the desired kink resistance thata neurovascular stent is required to possess. These two struts(sinusoidal 6 and S-shaped 2-4) repeat themselves (array) multiple timesfor the remainder of length of the device 100.

Due to the complexity associated with the 3-dimensional drawing of thestent 100 constructed of two halves 102, 104, the resulting strutstructures of the final assembled stent 100 is illustrated byoverlapping the two flat patterns (as if the stent has been flattened)of both parts 102, 104 on top of each other as shown in FIG. 6.

In other embodiments, the stent 100 can be constructed with struts ofvarious geometries. Examples of few such variations are shown in FIG.7A-C. In one embodiment, a stent 200 includes a first half 202 and asecond half 204 having sinusoidal longitudinal struts and sinusoidalradial struts as shown by the flat pattern view in FIG. 7A. In anotherembodiment, a stent 300 includes a first half 302 and a second half 304having straight longitudinal struts and sinusoidal radial struts asshown by the flat pattern view in FIG. 7B. In a further embodiment, astent 400 including a first half 402 and a second half 404 havingstraight longitudinal struts and straight radial struts as shown by theflat pattern view in FIG. 7C.

In another embodiment, the stent 100 can be constructed using only onehalf (instead of two halves 102, 104 as above). An example of such stent500 using only one half is shown in FIG. 8. In this configuration of thestent 500, the longitudinal struts 5 slide over each other as the stentis compressed in radial direction to a smaller diameter therebyresulting in a dense mesh structure 110 as shown in FIG. 8. In order tomake this embodiment of stent 500 feasible inside a typical bloodvessel, the length of the struts should be as long as possible.

FIG. 9 shows a flat pattern view of a part of a stent device such asstent 100 and illustrates exemplary dimensions of stent 100 (e.g.,implemented according to any of the examples shown in FIGS. 2-8). Thedimensions of struts of a final assembled stent 100 can be anywhere from0.0005″ to 0.003″ in width depending upon the degree of flexibilitydesired. The gap between the radial struts can be anywhere from 0.002″to 0.100″ depending upon the degree of denseness desired. The take-offangle of the radial struts from the longitudinal strut can be anywherefrom 15° to 90° as shown in FIG. 9. The length of the radial strut canbe anywhere from 0.10″ to 0.50″ but not limited to this range. Thelength of the stent 100 can be anywhere from 10 mm to 60 mm. However aconstruction of a stent 100 of length beyond this range is entirelyfeasible. The diameter of the stent 100 can be anywhere from 2 mm to 7mm. However, this method of construction is scalable for the diametersgreater than 7 mm.

To construct this stent 100, first the flat patterns of each halves 102,1074 of the stent 100 are drawn using a CAD software, for exampleAutoCAD. The strut width in the flat pattern can be anywhere between0.0030″ to 0.0050″. The specification of the strut width depends uponthe wall thickness of the nickel-titanium hypotube that the stent 100 iscut from. The electronic flat patterns are then programmed into acomputerized laser-cutting equipment. After the equipment has beenprogrammed, it drives a powerful laser beam along the edges of thedesign pattern and thereby cuts the exact same pattern from thenickel-titanium hypotube. The laser-cut stent 100 goes through asequence of subsequent processes. Some of those include: stress-reliefheat treatment at 500° C. to remove stresses from the laser-cut parts,microblasting to remove the outside oxide layer, expansion to a largerdiameter by shape setting at 500° C., chemical etching andelectro-polishing to remove much of material to obtain the final strutwidth.

The overlapping of nitinol stents 100 to get a dense mesh has beendemonstrated before but only by deploying two finished stentsseparately, second stent inside the first one. The process of stentingan aneurysm in two separate deployments not only increases the clinicalrisks associated with the deployment but also requires the catheteraccess through the first deployed stent.

One or more embodiments of the present disclosure facilitate thefeatures of two overlapped-stents in one stent. Advantageous features ofone or more embodiments of the present disclosure are the process ofassembling the stent 100 using two parts 102, 104 and the process ofjoining the two parts together at a location such as location 112 asdescribed herein. The stent 100 described in one or more embodiments ofthe present disclosure facilitate a dense mesh across the neck of ananeurysm using only a single deployment hence reducing the clinicalrisk. Since there is no second deployment involved with this stent 100,it eliminates the requirement of catheter access through the deployedstent.

In one embodiment of a process of joining the two parts 102, 104, thelongitudinal struts of the respective parts are aligned and wrapped(e.g., using a radiopaque marker) that could be in the form of a tubesuch as a platinum marker band as shown in FIG. 10A or a wound coil suchas a platinum coil as shown in FIG. 10B. After the process of wrappingthe struts, the remaining space inside the tube or coil may be filledwith a solder to enforce the joining of the two struts as shown in FIGS.11A-B. In some embodiments, a tube such as a platinum marker band may bemechanically crimped prior to filling the inside of the space with thesolder as shown in FIG. 12. Alternatively, the tube may be crimped and asolder may not be applied, or the filling of the space with the soldermay be performed prior to crimping the tube.

In the final set of processes, additional radiopaque markers (platinumor gold material) may be added at desired locations of the stent 100using the method of crimping or soldering. In the final assembly thestent is then mounted on a delivery system and loaded inside anintroducer sheath.

Advantageously, since the two parts 102, 104 of an assembled stent 100are free to slide inside one another, the stent 100 exhibits excellentresistance to kinking when deployed inside a tight curve. Anotheradvantageous feature of one or more embodiments of the presentdisclosure is the ease of manufacturability of the stent 100.

Embodiments described herein illustrate but do not limit the disclosure.It should also be understood that numerous modifications and variationsare possible in accordance with the principles of the presentdisclosure. Accordingly, the scope of the disclosure is best definedonly by the following claims.

What is claimed is:
 1. A stent comprising: a first longitudinallyextended cylindrical-shaped member, the first longitudinally extendedcylindrical-shaped member comprising a plurality of first sinusoidallongitudinal struts and an array of first sinusoidal radial strutsextending between the first sinusoidal longitudinal struts; wherein thestent comprises an overlapping region to form a dense mesh; and whereinthe first longitudinally extended cylindrical-shaped member furthercomprise S-shaped struts that connect to and extend from a correspondinglongitudinal central strut towards a corresponding longitudinal edgestrut, curve around to extend towards the corresponding longitudinalcentral strut, and curve around to extend to and connect to thecorresponding longitudinal edge strut.
 2. The stent of claim 1, whereinthe overlapping region comprises a part of the first longitudinallyextended cylindrical-shaped member overlapping around another part ofthe first longitudinally extended cylindrical-shaped member.
 3. Thestent of claim 1, wherein the overlapping region comprises more thanhalf of an outer surface of the stent.
 4. The stent of claim 1, whereinthe first longitudinally extended cylindrical-shaped member has aC-shaped cross-section, wherein the stent further comprises: a secondlongitudinally extended cylindrical-shaped member having a C-shapedcross- section, the second longitudinally extended cylindrical-shapedmember comprising a plurality of second sinusoidal longitudinal strutsand an array of second sinusoidal radial struts extending between thesecond sinusoidal longitudinal struts; wherein the overlapping region isformed by overlapping at least a part of the first longitudinallyextended cylindrical-shaped member and at least a part of the secondlongitudinally extended cylindrical-shaped member when assembled; andwherein the second longitudinally extended cylindrical-shaped memberfurther comprises S-shaped struts that connect to and extend from acorresponding longitudinal central strut towards a correspondinglongitudinal edge strut, curve around to extend towards thecorresponding longitudinal central strut, and curve around to extend toand connect to the corresponding longitudinal edge strut.
 5. The stentof claim 4, wherein the first longitudinally extended cylindrical-shapedmember and the second longitudinally extended cylindrical-shaped memberare assembled, and wherein the second longitudinally extendedcylindrical-shaped member is disposed within the first longitudinallyextended cylindrical-shaped member.
 6. The stent of claim 4, wherein thefirst longitudinally extended cylindrical-shaped member and the secondlongitudinally extended cylindrical-shaped member are aligned such thatan opening of the first longitudinally extended cylindrical-shapedmember and an opening of the second longitudinally extendedcylindrical-shaped member are on opposing sides of the stent radially.7. The stent of claim 4, wherein the first longitudinally extendedcylindrical-shaped member and the second longitudinally extendedcylindrical-shaped member are attached at a joining location comprisinga part of the first sinusoidal longitudinal struts and a part of thesecond sinusoidal longitudinal struts.
 8. The stent of claim 7, whereinthe first longitudinally extended cylindrical-shaped member and thesecond longitudinally extended cylindrical-shaped member are attached atthe joining location by solder around the part of the first sinusoidallongitudinal struts and the part of the second sinusoidal longitudinalstruts.